Variable pitch airscrew



Dec; 27, 1938. I P. P. RATIE VARIABLE PITCH AIRSCREW Filed Oct. 51,.1935 2 Sheets-Sheet 1 :9 7 2e" r 4E 25" as 2 4o 41 4o l Raft Dec. 27,1938. P. P. RATIE 2,141,552

VARIABLE PITCH AIRSCREW Filed 001;. 51, 1935 2 Sheets-Sheet 2 PatentedDec. 27, 1938 UNI-TED STATES 2,141,552 -VARIABLE r'rrcn AmscaEw' PierrePain Rati,

Montrouge, France, 'assignor to Societe dEtudes pour lAviation (S. E. P.A.)

Montrouge, France Application glctober 3 1, 1935, Serial No. 47,698

France May 31, 1935 ,1 Claim. -(c1. 170-162) The present inventionrelates to an airscrew, the

pitch of which is automatically variable during flight and capable ofassuming two main positions, and is characterized in that the pivotal 5movement of the blades, for ensuring the variation of the pitch, iseffected by means of a controlling screw or wind-wheel withinterposition of a gearing-down device.

In a form of construction, the controlling screw is arranged co-axiallywith front of'the latter.

Abutments of large pitch and small pitch limit the angular displacementoi. the blades.

For avoiding shocks at the end of the displacement, a friction clutch isprovided which constitutes a torque limiting device acting in bothdirections. This friction clutch is particularly fitted up on the hub ofthe controlling screw.

The blades of the controlling screw are preterably adjustable inposition.

The invention further relates to other particular points which willappear'from the following description with reference to the accompanyingdrawings, given by way of example only, in which: Fig. 1 'is anexplanatory'section of the blades of the controlling screw and airscrew.

Fig. 2 is a side elevation of the device showing the parts in section.according to line 11-11 of Fig. 3 looking in the direction of thearrows, this section showing a form of construction of an airscrew madeaccording to the invention. Fig. 3 is a front elevation showing theparts in section according to line ILL-III of Fig. 2. Fig. 4 is a planview with partial section corre- 1 sponding to Fig. 2 and showing theabutment device of the blades.

The drawings show a tractor airscrew which rotatesin a counterclockwisedirection for an ob- 40 server placed behind this airscrew. Thecounterclockwise direction will be designated by the expressionleft-hand direction". If the controlling screw is manually moved towardsthe left (the engine of the airplane being stopped); the blades pivottowardspthe direction of the largest pitch. On the contrary, if thecontrolling screw is' moved towards the right, the blades pivot towardsthe direction of the smallest pitch. When the engine rotates screw inthe lefthand direction, the rotation of the controlling screw relativelyto that of this airscrew, is being considered. In other words, when thespeed of rotation of the controlling screw, which rotates in the samedirection as that right-hand direction. screw rotates at the theairscrew and in .crease of the pitch).

rection of the stream arrows F" and F respectively, and, in both theseby driving the airoi the airscrew, is greater than the speed ofroairscrew, the direction of rotation of this controlling screw will bedesignated by the expression When the controlling same speed as that ofthe airscrew, the blades do not pivot and the pitch remains at adefinite value. 1v

. Referring more particularly to Fig. 1, this flgure shows in section ablade I of the controlling screw or wind wheel and a blade 2 of theairscrew.

Thedirection of advance of the airplane is shown by the arrow F Thearrows F and F respectively indicate the direction'of retardation of thecontrolling screw I relatively to the airscrew 2 (right-hand directioncausing the reduction of the pitch), and the direction of leads oradvance of the controlling screw l relatively to the airscrew 2(left-hand. direction causing in- As indicated in Fig. 1, the streamlines on the controlling-screw I have variable inclinations according tothe working speed of airscrew 2 and the speed of translation. For asection I, situated at a certain distance from the axis of rotation theinclination is the component of the tangential speed and of the speed oftranslation. The suction of the airscrew on the controlling screwmodifies very slightly this component;

When the airplane is on-the ground and stationary, the direction of thestream lines on the controlling screw I is indicated by the arrow F;this direction is such that the controlling screw retards relatively tothe airscrew and moves the blades up to the small pitch abutment. Whenthe airplane flies off or when it ascends, the dicases, the blades ofthe airscrew are alwaysheld in the small pitchposition.

When the airplane is flying horizontally or slightly dives, if theworking speed of the engine is reduced, the controlling screw I owing toits inertia, rotates more rapidly than the airscrew 2, this causingrotation of the blades substantially towards the large pitch position,and this to a certain extent. But, owing to the fact that the speed i ofthe airplane increases and that the working speed of the enginediminishes, the lead or advance per revolution is such that thedirection of the stream lines, which is indicated by arrow F causes thecontrolling screw I to rotate more rapidly than the airscrew (arrow F5),this causing the rotation of the blades towards the large pitch positionup to the abutment limiting the maximum large pitch. As long as theairplane is flying horizontally, the stream lines F hold the blades ofthe airscrew on the large pitch H abutment, as the controlling screwtends to rotate, in the direction of arrow F more rapidly than theairscrew.

This controlling screw has two distinct phases.

lines is indicated by the screw exceeds a certain value, thecontrolling.

screw supplies a torque on the airscrew shaft and increases the drag ofthe airplane. The controlling screw acts as driving device, and this isthe advance or lead phase viz: that of the large pitch. 1

It will therefore be seen from the statement, that the pitch of theairscrew is function of its lead per revolution.

The changes of flight in both directions; in fact, contrarily to whathas been stated above, it sumces, for obtain-' ing the small pitch, toascend and to rapidly open the throttle in order that the controllingscrew, by its inertia, begins to retard, then, the lead per revolution,when ascending, considerably diminishing, the controlling screwcontinues to retard up to the small pitch abutment.

Figs. 2 and 3 illustrate a form of construction of an airscrew, thepitch of which is automatically variable and controlled by a controllingscrew 5.

The hub H] of the airscrew is connected .to the shaft or driving plate Hand is provided with a plurality of tubular arms i2 in which thebladeslof the airscrew are pivotally fitted.

On the hub Hi is screwed a crown it connected,

through the medium of bolts id, to a casing it in which the gearing-downmechanism is arranged. The casing it comprises front and rear walls lland i8 on which is secured, co-axially with the airscrew, a tubularsupport is constituting a journal, through the medium of balls 26, for acontrolling screw i. The blades of this controlling screw are adjustablein position and,

for that purpose, the roots of these blades are clamped between shellsor cheek members 2i drawn together by bolts 22. Moreover, the cheekmembers 2! are connected to a friction plate 23 constantly urged againstfriction washers 24 by rods 25 and springs 2a. The unit, constituted bythe controlling screw l, cheek members 2| and plate 23, is frictionallyconnected to the 'hub 25 journalled, through the medium of the balls 28,on the tubular support shaft iii.

This friction connection prevents sudden stoppage of the airscrew bladesreaching the position of maximum or minimum pitch. This frictionconnection constitutes a friction clutch avoiding any sudden movement ofthe blades, when a variation of the pitch takes place Moreover,

this connection constitutes a torque iimiting device. 7 v

The hub 25 is provided with teeth 2%; (so-axial with the driving shaftand meshing with a series of peripheral pinions 2i. Each pinion 2i isrigidly secured on a shaft 26 journalled, through ball bearings 29, onwalls ll and i6. Each shaft 28 carries a Worth 30 meshing with a wormwheel 36 rigid with a shaft 32 journalled within the casing IS. Theshaft .32 carries a worm 33 meshing with a worm Wheel 35 the hub 35 ofwhich is 'journalled, through the medium of ball bearings 36, in' thewalls of the casing. This pitch can be obtained during.

wind wheel hub 35 is internally provided with a screw thread forconstituting a nut angularly movable only, and which causes thedisplacements in translation of screws 3'! rigid with a plate or piston38 capable of moving in translation in a corresponding cylindricalbearing portion 39 of casing It. On piston 38 are pivoted links 30pivotally connected at their other end to eccentric studs H rigid withthe blade roots.

When the controlling screw 8 rotates at the same speed as the airscrew,no relative movements take place between'the toothed wheels 26 and 21,so that the piston 38 remains stationary, the airscrew preserving thesame pitch. Any relative displacement between the controlling screw andthe airscrew causes the displacement of the gearing down mechanism and amovement of translation of piston 38 in one direction or the other forincreasing or diminishing the pitch of the airscrew according tocircumstances.

It is obvious that the form of. construction described and illustratedis given herein by way of indication only and not in a limiting sense.All changes or modifications which do not alter in any way the'mainfeatures above set forth and the desired result, remain included in thescope of the present invention.

In Fig. 4 has been. more particularly illustrated the abutment system ofone of the links it which is pivoted, by a pin 68, on the piston 32% andby a stud M on the root of the corresponding blade. The part 62 of thelink dii presses, in the extreme positions of the blades, against theabutmentfit formed by an inner projection of the hub of the airscrew.

What I claim as my invention and desire to secureby Letters Patent is:

In a unit for aerial propulsion, comprising a variable pitch airscrew,of which is fixed during flight, mounted coaxially with said airscrewfor rotation in the same direction as and at the same or a greater orless speed than the latter, a shaft for rotatively supporting the windwheel, a connection mechanism between the Wind wheel and the airscrewfor moving the blades of said airscrew in one direction or the other inorder to modify the pitch of said blades when a diiference of speedexists between the wind wheel and airscrew in combination, abutments forlimiting the angular displacements of the blades-of the airscrew in thelarge pitch and small pitch positions, means for frictionally connectingsaid wind wheel and said shaft on which said wind wheel is mounted foravoiding, at the end of the displacement, shocks of the blades againstsaid abutments and which constitutes a device for limiting the torque inboth directions, andmeans for adjustably assembling, when on the ground,the blades of the wind wheel, the pitch of said wind wheel having suchvalue that the aerodynamic torque exerted on the same changes the speedthereof to eifect a relative rotary displacement of said relatively tosaid airscrew in one direction or the other, when, for one and the samespeed of rotation of the airscrew, the speed of translation of saidairscrew departs from a definite value, or when for one and the samespeed of translation of the airscrew, the speed of rotation of saidairscrew departs from a definite value.

PIERRE PAUL RATE.

a wind wheel the pitch

